Coherent illumination is being increasingly used in electrophotographic printing for image formation on photoreceptors. Unfortunately, the use of coherent illumination sources in conjunction with multilayered photoreceptors results in a print quality defect known as the "plywood effect" or the "interference fringe effect." This defect consists of a series of dark and light interference patterns that occur when the coherent light is reflected from the interfaces that pervade multilayered photoreceptors. In organic photoreceptors, primarily the reflection from the air/charge transport layer interface (i.e., top surface) and the reflection from the undercoat layer or charge blocking layer/substrate interface (i.e., substrate surface) account for the interference fringe effect. The effect can be eliminated if the strong charge transport layer surface reflection or the strong substrate surface reflection is eliminated or suppressed.
Methods have been proposed to suppress the air/charge transport layer interface specular reflection, including roughening of the charge transport layer surface by introducing micrometer size SiO.sub.2 dispersion and other particles into the charge transport layer, applying an appropriate overcoating layer and the like.
Methods have also been proposed to suppress the intensity of substrate surface specular reflection, e.g., coating specific materials such as anti-reflection materials and light scattering materials on the substrate surface and roughening methods such as dry blasting and liquid honing of the substrate surface. For example, photoreceptor substrate surfaces have been roughened by propelling ceramic and glass particles against a surface.
FIGS. 1 and 2 depict a prior art hollow cone spray nozzle 10 used in a conventional honing method to roughen the surface of photoreceptor substrates. The hollow cone spray nozzle 10 is composed of a housing 12 defining a channel 14, a round entry opening 16 where the honing composition enters the nozzle, and a round exit opening 18 where the honing composition exits the nozzle. FIG. 3 shows a graph depicting a representative particulate material spray distribution of the hollow cone spray nozzle of FIGS. 1 and 2. The phrase "distance along spray area" as used herein refers to an imaginary line along the largest dimension (e.g., length or width) of a surface impinged by the particulate material. For a cylindrical substrate, the phrase "distance along spray area" refers to an imaginary line along the longitudinal axis or length of the substrate. The graph in FIG. 3 is a rough approximation based on general principles, equipment literature and process observations. FIG. 3 indicates that a hollow cone spray nozzle produces a particulate material spray distribution having two peaks. When viewed from another perspective (see illustration of a hollow cone spray on page 1 of BEX catalog 45), the hollow cone spray nozzle produces a ring shaped particulate material spray distribution with a heavier particulate material impingement area encircling a region having lesser particulate material impingement.
Conventionally, four spray guns, each including a hollow cone spray nozzle of the type depicted in FIGS. 1 and 2, are used to propel a honing composition containing the particulate material toward a single substrate. It was discovered that when fewer than four spray guns are used, the substrate surface roughening time became longer and comparable roughness uniformity was not achieved. The resulting non-uniform surface roughness is manifested as a visible "barber pole" or "cauliflower" shaped defects on the substrate surface. Thus, there is a need, which the present invention addresses, for new methods to allow fewer spray guns to be used to roughen a substrate without lengthening the photoreceptor fabrication time or adversely affecting the substrate surface.
The following patents illustrate the honing process: Rasmussen et al., U.S. Pat. No. 5,573,445; Harada et al., U.S. Pat. No. 5,332,643; Hashiba et al., U.S. Pat. No. 5,238,467; and Herbert, U.S. Pat. No. 5,586,927, the disclosures of which are totally incorporated by reference.
A fan nozzle is disclosed in Shank, Jr., U.S. Pat. No. 5,365,702.
BEX Inc. catalog 45, page 1, depicts a flat spray, a full cone spray, and a hollow cone spray, the disclosure of which is totally incorporated herein by reference.